This invention relates to an automatic scanning circuit for determining or selecting the highest or lowest of a plurality of signals representative of any of several parameters such as temperature, pressure, vibration, etc.
In known automatic scanning circuits, such as the circuit described in U.S. Pat. No. 3,124,752, issued Mar. 10, 1964 to S. Thaler, a diode matrix is utilized to select the highest or lowest of the plurality of signals being scanned. Similarly, in U.S. Pat. No. 3,158,849, issued Nov. 24, 1964 to S. Thaler, a transistor matrix is used to perform this signal selection function and also to energize an indicating light identifying the selected signal. In both of these prior known automatic scanning circuits, each signal being scanned must include a dc component which varies directly as an ac component of the same signal, so that the selected signal will not be attenuated by the inherent voltage drop across the conducting diode or transistor. However, in these known signals scanning circuits, slight differences in the forward voltage drops of the diodes or transistors affect the switch-over point between signals of similar magnitude.